In recent years, the 3GPP (3rd Generation Partnership Project) group meeting has specified LTE-A (Advance) as an evolutionary communication system of LTE (Long Term Evolution), a high speed data communication technology for terminal devices such as cellular phones. The 3GPP group meeting has also investigated the specification of a communication system using a relay device for communication between a terminal device and a base station.
FIG. 21 shows an example configuration of a communication system according to a related technology. In FIG. 21, BS represents a base station, RN represents a relay node as a relay device, and UE represents a user equipment as a terminal device.
As shown in FIG. 21, for example, a related communication system includes the base station BS, the relay node RN, the user equipment UE1, and the user equipment UE2. In addition, the relay node RN is included in a cell, the communication area of the base station and the user equipments UE1 and UE2 are included in the communication area of the relay node RN. However, any of the user equipments UE, like the user equipment UE2, is not always included in the cell, the communication area of the base station BS. Here, FIG. 21 represents the communication system that includes the base station BS, the relay node RN, and two user equipments UE. However, the cell may include a plurality of relay nodes RN having a plurality of user equipments in the communication area.
In the aforementioned configuration of the communication system, for example, when data transmission between the base station BS and the user equipment UE1 is performed, the relay node RN relays data to perform data transmission/reception. Likewise, when data transmission is performed between the base station BS and the user equipment UE2, the relay node RN relays data to perform data transmission/reception. Regarding the modes of communication among the respective devices, furthermore, a communication mode between the base station and the relay node RN is different from the user communication mode between the relay node RN and the user equipment. The term “communication mode” used herein refers to information about a mode required for the reception procedure described later.
Next, the steps of the process carried out in the related communication system are described with reference to FIG. 22. FIG. 22 is a diagram illustrating the steps of the process in the related communication system. The user equipment UE shown in FIG. 22 is one included in the communication area of the relay node RN present in the cell of the base station BS. The user equipment UE may be either the user equipment UE1 or the user equipment UE2 shown in FIG. 21.
For example, as shown in FIG. 22, the base station BS generates a signal to transmit data to the relay node RN. The relay node RN receives the data from the base station BS and then performs the reception processing on the received data. Subsequently, the RN performs signal generation, or re-encoding, on the data subjected to the reception processing, followed by transmitting the data to a destination device, the user equipment UE, after predetermined processing delay. Subsequently, after receiving the data transmitted from the relay node RN, the user equipment UE carries out the reception processing on the data.
Although FIG. 22 describes the steps of the process carried out in a downlink (DL) from the base station BS to the user equipment UE, a similar process is also carried out using in a uplink (UL) where the user equipment UE is used as a source and the base station BS as a destination.
FIG. 23 illustrates an example of the transmission/reception frame in the related communication system. In FIG. 23, the user equipment UE1 shown in FIG. 21 is used as an example of the user equipment UE in a communication area of the relay node RN in the cell of the base station BS.
As shown in FIG. 23, for example, traffic for UE1 is included in one subframe when the base station BS sends data to the relay node RN. When sending the data from the base station BS to the relay node RN, control information, which represents a mode for communication from the base station BS to the relay node RN is stored in the head of the frame. Thus, the data is stored in the data area, followed by being sent to the relay node RN. Subsequently, the relay node RN carries out predetermined processing, such as reception processing of the received data and recoding processing. Here, the control information includes, for example, the frequency of an applied resource, modulation scheme, and coding scheme, which vary depending on the communication mode.
On the other hand, if the data is sent from the relay node RN to the user equipment UE1 after the predetermined process delay by the relay node RN, the control information or the like, which represents a mode of communication from the relay node RN to the user equipment UE1, is similarly stored in the head of the frame. The data is stored in the data area and then sent to the data area. In other words, the data sent from the base station BS to the relay node RN and the data sent from the relay node RN to the user equipment UE1 have different pieces of control information because of their communication modes between the devices, while their data areas store and send the same data.